Simplify the following expression: $k = \dfrac{5x}{8} - \dfrac{9x}{8}$
Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{5x - (9x)}{8}$ Combine like terms: $k = \dfrac{-4x}{8}$ Simplify by dividing numerator and denominator by 4: $k = \dfrac{-x}{2}$